Before we go to the OSI principle, do you know what OSI is? Open Systems Interconnect (OSI) Layer is a communication standard that is applied in computer networks. That standard is what causes all communication tools to communicate with each other through the network. The OSI reference model illustrates how information from an application software on a computer moves across a network media to an application software on another computer.The OSI reference model is conceptually divided into 7 layers where each layer has a specific network function. The Open Systems Interconnection (OSI) model was created by the International Organization for Standardization (ISO) which provides a structured logic framework for how data communication processes interact through networks. This standard was developed for the computer industry so that computers can communicate on different networks efficiently.

7 Layer on OSI Model

Each layer is specifically responsible for the data communication process. For example, one layer is responsible for establishing connections between devices, while another layer is responsible for correcting “errors” during the data transfer process.

The OSI Layer Model is divided into two groups: “upper layer” and “lower layer”. “Upper layer” focuses on user applications and how files are represented on a computer. For Network Engineers, the main part of his concern is the “lower layer”. Lower layer is the essence of real-time data communication over a network.

The main purpose of using the OSI model is to help network designers understand the function of each layer associated with data communication flow. Includes the types of network protocols and transmission methods.

The function of 7 Layer on OSI Layer

1. Physical Layer | Layer 1 (Devices)

Berfungsi untuk mendefinisikan media transmisi jaringan, metode pensinyalan, sinkronisasi bit, arsitektur jaringan (seperti halnya Ethernet atau Token Ring), topologi jaringan dan pengabelan. Selain itu, level ini juga mendefinisikan bagaimana Network Interface Card (NIC) dapat berinteraksi dengan media kabel atau radio.

Protokol yang berada dalam lapisan ini :

Tidak mempunyai protokol yan spesifik di layer ini, bertanggung jawab atas proses data menjadi bit dan mentransfernya melalui media, seperti kabel, dan menjaga koneksi fisik antar sistem, pada layer ini hanya mengirimkan bit bit data.

2. Data-Link Layer | Layer 2 ( MAC, Error Detection )

Serves to determine how the data bits are grouped into a format called a frame. In addition, at this level error correction, flow control, hardware addressing (such as Media Access Control Address (MAC Address)) occur, and determine how network devices such as hubs, bridges, repeaters, and layer 2 switches operate. The IEEE 802 specification, divides this level into two child levels, namely the Logical Link Control (LLC) layer and the Media Access Control (MAC) layer.

Protocols that are in this layer:

– PPP (Point to Point Protocol)

The protocol used for point to point on a network.

– SLIP (Serial Line Internet Protocol)

The protocol used to connect serially.

3. Network Layer | Layer 3 (Logical addressing, Routing)

Serves to define IP addresses, create headers for packets, and then do routing through internetworking using layer-3 routers and switches.

Protocols that are in this layer:

– IP (Internetworking Protocol)

The transmission mechanism used to transport data in packets is called datagrams.

– ARP (Address Resulotion Protocol)

The protocol used to find out IP addresses based on the physical address of a computer.

– RARP (Reverse Address Resulotion Protocol)

The protocol used to find out the physical address via a computer IP.

– ICMP (Internet Control Message Protocol)

The mechanism used by a number of hosts to send datagram notifications that have problems with their hosts.

– IGMP (Internet Group Message Protocol)

Protocol used to provide simultaneous message facilities to recipient groups.

4. Transport Layer | Layer 4 (Reliable or unreliable delivery)

Serves to break data into data packages and assign serial numbers to these packages so that they can be rearranged on the destination side after they are received. In addition, at this level also makes a sign that the packet was received successfully (acknowledgment), and retransmits the packets lost in the middle of the road.

Protocols that are in this layer:

– TCP (Trasmission Control Protocol)

Protocol that provides full transport layer services for applications.

– UDP (User Datagram Protocol)

Connectionless protocols and process-to-procces that only add port addresses, error control and length of data information on the layer above it.

5. Session Layer | Layer 5 (Keeping data separate from different application)

Serves to define how connections can be made, maintained, or destroyed. In addition, at this level also carried the name resolution.

Protocols that are in this layer:

– NETBIOS

Functioning as a message broadcast means that it allows the user to send a single message simultaneously to another connected computer.

– NETBEUI (NETBIOS Extended User Interface)

It works just the same as NETBIOS only a little further developed by adding functions that allow it to work with a variety of hardware and software.

– ADSP (AppleTalk Data Stream Protocol)

This protocol functions to monitor the flow of data between two computers and to check the data flow is not interrupted.

– PAP (Printer Access Protocol)

Postscript printer functions for access to the AppleTalk network and to control how communication patterns between nodes.

– SPDU (Session Data Protocol unit)

Serves to support the relationship between two user service sessions.

6. Presentation Layer | Layer 6 (How data is presented)

Function to translate data that is to be transmitted by the application into a format that can be transmitted over the network.

Protocols that are at this level:

– TELNET

The protocol used for remote access to a host, data runs in another text.

– SMTP (Simple Mail Transfer Protocol)

One of the common protocols used for sending e-mail on the internet or for sending data from the sending computer e-mail to the recipient’s e-mail server.

– SNMP (Simple Network Management Protocol)

The protocol used in a network management.

7. Application Layer | Layer 7 (User Interface)

Serves as an interface with applications with network functionality, regulates how applications can access the network, and then creates error messages

Protocols that are in this layer:

– HTTP (Hyper Text Transfer Protocol)

The protocol used to transfer documents and the web in a web browser, via www. HTTP is also a protocol that requests and answers between client and server.

– FTP (File Transfer Protocol)

An internet protocol that is spent at the application layer which is a standard for transferring computer files between machines on an internet network.

– NFS (Network File system)

Network protocol that allows users on a client computer to access files over the network in the same way as the local storage they access.

– DNS (Domain Name System)

The protocol used to assign a domain name to an IP address to make it easier to remember.

– POP3 (Post Office Protocol)

The protocol used to retrieve mail from a mail transfer agent, which will eventually be downloaded to the local network.

– MIME (Multipurpose Internet Mail Exension)

The protocol used to send binary files in text form.

– SMB (Server Messange Block)

The protocol used to transfer file servers to DOS and Windows.

– DHCP (Dynamic Configuration Protocol)

A service that assigns an IP number to a computer that requests it automatically.

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